Despite continuously growing literature that emphasises the significant role of students' agency in classroom activities, the construct of agentic engagement has received scant attention in recent empirical research. Drawing from the self-determination theory, the present study aims to determine the relationship between teacher autonomy support and agentic engagement, and explore whether personal best goals mediate such associations. For this purpose, using a cross-sectional design, data from 536 university students in northern Malaysia were analysed. The associations among the constructs were evaluated using structural equation modelling. The empirical results indicate that students' perceptions of teacher autonomy support were associated with personal best goals and agentic engagement. In addition, the findings suggest that personal best goals significantly mediate the relationship between teacher autonomy support and agentic engagement. These findings highlight the critical role of personal best goals as a mechanism by which an autonomy-supportive teaching style facilitates students' agency during their learning activities.